In later stages (fig. 113 C) the blastopore becomes closed, and the mantle region increases in length as compared with the remainder of the body. The ventral halves of the funnel, each in the form of a half tube, coalesce together to form a single tube (_inf_) in the same manner as in Sepia. A shallow proctodæum (_an_) is formed between the two branchiæ. The eyes (_oc_) stand out as lateral projections, and the arms become much longer. [FIG. 113. THREE EMBRYOS OF A CEPHALOPOD WITH A VERY SMALL YOLK-SACK. (After Grenacher.) _a._ blastopore; _br._ branchiæ; _inf.1_ and _inf.2_ posterior and anterior folds of the funnel; _g.op._ optic ganglion (?); _oc._ eye; _wk._ white body; _ac._ auditory pit; _os._ stomodæum; _an._ anus; _mt._ mantle; 1, 2, 3. 1st, 2nd, and 3rd pairs of arms. Still later a fourth pair of arms is added as a bud from each of the posterior pair, and with the growth in length of the arms the suckers make their appearance. The mouth is gradually carried up so as to be surrounded by the arms. The ciliation of the surface becomes more extensive. During the whole of the above development the interior of the embryo is filled with yolk, although no external yolk-sack is present. The internal yolk-sack falls into three sections; a cephalic section, a section in the neck, and an abdominal section. Of these, that in the neck is the first to be absorbed. The cephalic portion fills out the ventral protuberance already spoken of. The hinder section becomes occupied by the liver which exactly fits itself into this space as it absorbs the material previously there. It will be convenient at this point to complete the account of the Cephalopoda by a short history of their germinal layers, and by a fuller description of the mantle, shell, and funnel than that given in the preceding pages. [FIG. 114. LONGITUDINAL VERTICAL SECTION THROUGH A LOLIGO OVUM WHEN THE MESENTERIC CAVITY IS JUST COMMENCING TO BE FORMED. (After Bobretzky.) _gls._ salivary gland; _brd._ sheath of radula; _oe._ oesophagus; _ds._ yolk-sack; _chs._ shell-gland; _mt._ mantle; _pdh._ mesenteron; _x._ epiblastic thickening between the folds of the funnel.]